The phenomenon of the seasons

Contrary to popular belief, the phenomenon of the seasons – or the periodic change of climate over the months – is not a result of Earth approaching or moving away from the Sun. Seasonal climatic variations are due to the slight tilt of the Earth, which spins like a top tilted at an angle of 23.5 degrees in relation to its orbital path. This tilt explains why one hemisphere receives more sun than the other at a given time of year. If the Earth’s axis were not tilted, there would be no seasonal variations in temperature. Our climate in October would more or less resemble our climate in March.

Spring equinox

On March 20 or 21, day and night are of equal duration in the Northern hemisphere, which is why it is referred to as the spring equinox. On that day, the Sun rises exactly in the east and sets exactly in the west.

Summer solstice

In summer in the Northern hemisphere, the Sun is high in the sky and it is hot. The summer solstice, which occurs on June 21, is the longest day of the year.

Autumnal equinox

On September 22 or 23, day and night are of equal duration in the Northern hemisphere, which is why it is referred to as the autumnal equinox. On that day, the Sun rises exactly in the east and sets exactly in the west.

Winter solstice

In winter in the Northern hemisphere, the Sun is low in the sky and it is cold. The winter solstice, which occurs on December 21 or 22, is the shortest day.